Introduction

Air Handling Unit Factory Acceptance Test is a part of the HVAC validation lifecycle. It consists of the documented testing of the AHU at the vendor facility. The goal is to check that meets all the specifications before at the manufacturer site.

According to the Annex 15 of EU GMP:

This can reduce the always short terms available for validation activities.

The Standards

Testing will check that User Requirement Specifications (URS) are met. We will cover how to prepare a URS for an AHU in a separate post.

AHU manufacturers usually design the units to accomplish many legal specifications. For our concern, we will focus on FAT testing on the following:

• EN 1886, mechanical construction.
• RS 6/C/011-2018, hygienic construction. This is free and can be downloaded from here: https://eurovent.eu/?q=articles/eurovent-publishes-guidebook-air-handling-units

Testing

Basic tests to perform will be those to check standards accomplishment and those that may compromise the future operation.

The following are recommended, but not limited, proposed testing:

1. Mechanical Strength of the casing

The purpose of this test is to verify the Mechanical strength of the AHU casing in accordance with EN1886. The objective is to demonstrate that structurally the casing is not deformed in operation. Air handling unit casings are categorised into classes (D1 to D3). D1 is the most restrictive class with a maximum reflective deflection of 4 mm/m. This is the classification we usually specify for our AHU.

Deflection shall be measured within an uncertainty of +/‐ 0.5 mm whilst the air handling unit is operating at its normal design condition; for example referring to the following figure, X’X’’ measured for span R’S’, XX’’ is measured for span PQ.

The test shall be deemed to pass if deflection is within the limit of the class D1 of EN1886 (i.e. 4 mm/m maximum relative deflection at 700 Pa)

The instrument we will use is a calibrated calliper.

2. Air Tightness

The purpose of this test is to verify the airtightness of the AHU at 700Pa positive pressure and at 400Pa negative pressure.

The unit to be tested shall be put up in the plane in which it is intended to operate with its sections connected or joined by the method given in the installation instructions.

Where it is necessary to fit blanking plates, the plates shall be fitted by a similar method to that of the intended installed joint. Openings for electrical, air or water services shall be closed prior to testing. Dampers shall be dismounted before testing or fitted with blanking plates if the damper is inside.

The test apparatus shall be as shown below figure (figure shows the negative pressure setting), using a fan with duty at least capable of meeting the anticipated leakage rate at the respective test pressure(s). If the air handling unit is too large for the capacity of the leakage test apparatus (accuracy ± 3,0 %), or a restriction of access for delivery requires that the unit should be tested in sections or subassemblies.

1 AHU under test

2 AHU test pressure gauge

3 Bleed valve as an alternative to variable speed fan

4 Variable-speed fan

5 Flow measuring device

6 Inlet plate

7 Outlet plate

The test shall be performed in this way:

Turn on the test apparatus fan unit and adjust until the static test pressure inside the test unit is within 5 % of the specified figure. Keep this pressure constant for 2 minutes, and do not record any readings until the pressure has stabilized. Record the pressure drop across the orifice (to calculate the flow rate) and the test pressure.

To determine the allowable leakage rate, calculate the casing surface area from the nominal external dimensions, including the area of the blanked inlet and outlet airflow aperture. The area of components which does not form part of the airtight casing shall be excluded. The maximum allowed leakage rate shall in accordance with class L1 (0.22 l x s‐1 x m‐2  @ 700 Pa positive pressure) and  (0.15 l x s‐1 x m‐2  @ 400 Pa negative pressure). Determine the maximum allowable leakage and relate it to the casing area of the unit under test. The unit shall be deemed passable if the recorded leakage rate is not greater than the allowable leakage rate.

3. Air Flow and Pressure Test

With this test, we will evaluate the actual air volume and static pressure delivered by the installed fan when running at the design RPM. Actual fan curve will be plotted and interaction of the fan curve with the system curve will determine the actual fan operating point. Actual fan operating point shall not deviate +/‐ 5% on the air volume and +/‐ 10 % on the static pressure.

We will measure Air velocity by using and electronic revolving‐vane anemometer capable to automatically average the readings. Pressure by using an electronic micromanometer. We will need as well a damper to modify the system pressure.

So, the test procedure will start by turning on the fan at the design fan speed. We have to record for each damper position (minimum 3 positions) the following data :

• Air velocity in the duct
• Discharge static pressure inlet
• Static pressure

We will record the data with at least 3 damper opening and we will be sure that the design fan system line falls within the minimum and maximum damper opening. We have also to measure the duct area for the final calculations.

Following, we will plot on a graph the measured fan curve and the actual system curve. The point of intersection of the design system curve and the actual fan performance curve determines the actual flow volume and static pressure at the design condition.

Finally, we will determine the air volume and static pressure difference between the actual fan operating point and the design fan operating point. The unit shall be deemed to pass if the air volume and static pressure obtained at the intersection between the actual fan curve and the design system curve is within the allowable rate.

4. Vibration Test

With this test, we will evaluate the vibration level at the actual fan speed. The measured vibration level shall not exceed the limits indicated in the ISO 14694:2003 for class BV‐3 (see table below) – Vibration levels limit for test manufacturer’s workshop.

5. Other Tests

The list of tests can increase as much as you think is critical to check at the manufacturer factory. Simply use your URS to select what you want to test. I would recommend the following additional checks or visual inspections:

• Unit dimensions, number of sections. Check the available space in the plant room and accesses.
• All parts are accessible for cleaning and maintenance. Any maintenance person can reach manually at any inner casing surface.
• Coil access, droplet separator removal.
• Sufficient slope in condensate trays.
• Doors hinges and closing system.
• No instruments are in a door or removable access.
• Easy filter change.
• Siphon height.
• Identification of piping connections, supply, return, fans, filters, etc.
• Instrumentation, differential pressure gauges, airflow, pressure switches, etc.
• Grounding.

And that is all. With these simple guidelines, I hope you can perform a satisfactory FAT of your new recently acquired Air Handling Unit and avoid not desired consequences of bad design and construction. As well as it helps to comply with the quality requirements.